Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

NORDITA , anything interesting?

  1. Nov 29, 2012 #1
    I believe the Nordita Perspectives of Fundamental Cosmology Conference ends today, did anybody go. Anything interesting to report to PF?
  2. jcsd
  3. Nov 29, 2012 #2


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    Well francesca is a PF member and she attended and gave a talk. She might not see this thread but you could write her a PM and see if she is not too busy and wants to post some report here. She might not have time and might decline but it wouldn't be wrong to ask.

    Another thing would be just to go to the NORDITA conference website and look at francesca's set of slides. It is a nice long set of slides. I don't know how she could have fit it into an hour talk. It reviews the history of QG and the application to quantum cosmology and then talks about various people's recent quantum cosmology work.

    I'll get the main conference link in case you don't have it.
    Here is the main link:
    You click on "speaker list" and you get a list of talks, many of which have PDF slides links.
    You scroll down to near the end where Francesca's talk is listed and click on "slides":
    She did a good job, I was impressed with how much she covered in her talk.
    Last edited: Nov 29, 2012
  4. Nov 30, 2012 #3
    Thanks Marcus
  5. Dec 1, 2012 #4


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    I wish I could give you some more substantial news from the Fundamental Cosmo conference
    but here is a little something.
    It is a little over halfway thru Francesca's slides where she mentions the
    MUKHANOV-SASAKI equation in it's LQC-corrected form, in parallel with the effective LQC version of Wheeler-Dewitt.

    This has just come on the scene and I think it will revolutionize LQC. When the effect of matter is included in the LQC model, using M-S equation, the model will bounce much sooner when the density is still much lower.

    Francesca refers to a paper she did with Cailleteau, Barrau, Grain, where they put the Mukhanov-Sasaki. But for me the big impact only appears when you look at the very recent (November) paper of Ed Wilson-Ewing.

    It is strange that Ed W-E was not presenting this paper at the NORDITA conference. Maybe the work is too new and he does not have slides, or he didn't get invited. This will surely get presented at the Loops 2013 conference. He seems to be saying that the bounce happens when the energy density is still only one billionth of Planck density.
    Consistency of holonomy-corrected scalar, vector and tensor perturbations in Loop Quantum Cosmology
    Thomas Cailleteau, Aurelien Barrau, Julien Grain, Francesca Vidotto
    (Submitted on 28 Jun 2012)
    Loop Quantum Cosmology yields two kinds of quantum corrections to the effective equations of motion for cosmological perturbations. Here we focus on the holonomy kind and we study the problem of the closure of the resulting algebra of constraints. Up to now, tensor, vector and scalar perturbations were studied independently, leading to different algebras of constraints. The structures of the related algebras were imposed by the requirement of anomaly freedom. In this article we show that the algebra can be modified by a very simple quantum correction, holding for all types of perturbations. This demonstrates the consistency of the theory and shows that lessons from the study of scalar perturbations should be taken into account when studying tensor modes. The Mukhanov-Sasaki equations of motion are similarly modified by a simple term.
    5 pages


    The Matter Bounce Scenario in Loop Quantum Cosmology
    Edward Wilson-Ewing
    (Submitted on 27 Nov 2012)
    In the matter bounce scenario, a dust-dominated contracting space-time generates scale-invariant perturbations that, assuming a nonsingular bouncing cosmology, propagate to the expanding branch and set appropriate initial conditions for the radiation-dominated era. Since this scenario depends on the presence of a bounce, it seems appropriate to consider it in the context of loop quantum cosmology where a bouncing universe naturally arises. It turns out that quantum gravity effects play an important role beyond simply providing the bounce. Indeed, quantum gravity corrections to the Mukhanov-Sasaki equations significantly modify some of the results obtained in a purely classical setting: while the predicted spectra of scalar and tensor perturbations are both almost scale-invariant with identical small red tilts in agreement with previous results, the tensor to scalar ratio is now expected to be r≈ 9 x 10-4, which is much smaller than the original classical prediction. Finally, for the predicted amplitude of the scalar perturbations to agree with observations, the critical density in loop quantum cosmology must be of the order ρcrit ~ 10-9 ρPlanck.
    8 pages
    Last edited: Dec 1, 2012
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook